When a patient suffers cardiac arrest, it is required to initiate life-saving techniques as soon as possible, preferably within 8 minutes. If there is no blood flow for more than about 15 minutes, the brain and other organs will normally develop irreparable damage.
A previously known type of CPR is to manually compress the breastbone of the patient and to mechanically inflate the lungs of the patient.
A mechanical device for performing mCPR is known in Sweden under the trademark LUCAS® and is described in the documents SE 521141 and WO 2005/046558. Generally, the device comprises a piston that presses a cup shaped plate towards the sternum to compress the heart and thorax positioned there below in a compression stroke. The plate may be attached to the body of the patient, for example by means of a suction pressure inside the cup shaped plate or by means of an adhesive. When the plate is actively withdrawn, the sternum is lifted in order to forcedly expand the thorax of the patient. The movement stroke of the plate may be about 20% of the vertical distance over the thorax. The stroke cycle may be about 100 strokes/min. The active stroke may take about 0.1 seconds both down and up and there may be about 0.2 seconds of rest between each movement.
When performing mCPR with the above-mentioned device, oxygen may be supplied via a tracheal tube inserted into the trachea of the patient. The tracheal tube comprises a central channel with a diameter of about 6-10 mm and several small channels arranged in the wall of the tube. The tracheal tube may be of the Boussignac type, for example a tracheal tube included in a Boussignac Cardio Pulmonary Resuscitation System sold by VYGON, BP 7-95440 Ecouen, France under Ref 6508.70. Such a tracheal tube is for example disclosed in U.S. Pat. No. 5,036,847.
The small channels can be used for different purposes. In the present context they may be used for supplying oxygen gas to an area adjacent the bronchi of the patient. In this way, sufficient amount of oxygen is supplied to the patient and sufficient amount of carbon dioxide is removed by the volume changes developed during the thorax compression and by eliminating the “dead space” in the ventilation.
EP 0029352 A1 discloses a cardiopulmonary resuscitator comprising a reciprocatable cardiac compressor means for cyclically compressing a patient's chest and a ventilating means for inflating the patient's lungs to a benign limiting pressure such as between 10 and 60 cm of water over a period encompassing at least one and preferably three cycles of the compressor means. The resuscitator includes ventilator output control means for (i) preventing retrograde and exhale flow from the patient's lungs during the systolic portion of the cycle of the compressor means thus providing for a pressure increase in the patient's lungs due to compression of the patient's chest to a level well above that of the limiting pressure, for example to between 75 and 200 cm water, and (ii) periodically venting the patient's lungs, for example for two cycles of the compressor means.
One of the problems of CPR that needs attention is to obtain a sufficient pressure differential between the aorta and the right atrium, so that a sufficient coronary perfusion pressure is obtained, otherwise the heart will suffer permanent damage. Another problem is to obtain a low pressure in the pulmonary veins wherein blood is transported from the body and into the thorax, so that a sufficient refill of the thorax is obtained.
In an article entitle: “Continuous intratracheal insufflation of oxygen improves the efficacy of mechanical chest compression-active decompression CPR”, published in Resuscitation 62 (2004), pages 219-227, the authors, Stig Steen et al, advocate that a continuous insufflation of oxygen (CIO) is superior over intermittent positive pressure ventilation (IPPV). The article shows that CIO results in an improved coronary perfusion pressure compared to IPPV.
However, there is a need for still better performance of mCPR.